Friday, October 4, 2013

Swallows having trouble in the cold

Back in May, we had a cold snap mid-month with strong winds and temperatures barely above zero for several days in a row. I discussed the effect this had on the warblers in a post earlier this year, but one group of birds was hit even harder by the cold snap: swallows.

Swallows are extremely good at what they do - hoovering up flying insects. Unfortunately, this comes at a price, and that price is that they are utterly incompetent at virtually everything else. So when unseasonably cold temperatures and strong winds ground most of their prey, swallows have little choice but to eke out enough to survive from whatever is left. This often means travelling to warm sheltered water bodies - a perfect description of your typical sewage lagoon.

When I first arrived at the Blenheim Sewage Lagoons during the cold snap, it was immediately obvious that the swallows were having trouble. A number of individuals were dead on the road from cars, and several more were sitting on the road exhausted. Once I climbed the dike to get a look into the lagoons themselves, I saw an impressive spectacle:

Huge numbers of swallows (mostly Trees) were feeding just over the surface on the leeward sides of the larger ponds, with lots more resting exhausted on vegetation and the ground around the ponds.

Interestingly, all the Purple Martins were perched. I assume that, being much larger than the other swallows, they weren't able to get enough energy from feeding to even replace that used by flying.

Two larger birds were mixed in with the swallows: Black Terns! One can be seen in the video below, apparently foraging for flying insects just like the swallows. Apologies for the poor video quality - the wind was so strong that it was impossible to hold the camera steady, even laying down.

I estimated about 1500 swallows the first time I visited, and 2000 on my second trip the next day. You can see exact numbers and the other birds I saw at the eBird checklists below:

Luckily, the cold eventually left and most of the birds seemed to survive. I'd hate to have seen what would happened to the swallows and all the other insectivores with another couple of cold days. Given that this didn't happen, this experience was one of the highlights of my spring.

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